Non-curling multilayer material



United States Patent 3,300,313 NQN-CURLKNG MULTILAYER MATERIAL Marcel Nicolas Vrancken, Eerchem-Antwerp, Daniel Aloi's Claeys, Marisol-Antwerp, August Jean Van Paesschen, Hove, and Jan Bernard Lambrechts, Ant- Werp, Belgium, assignors to Gevaert Photo-Producten N.V., Mortsel-Antwerp, Belgium, a company of Belgiuln No Drawing. Filed Aug. 12, 1963, Ser. No. 301,667 4 Claims. (Cl. 96-87) This invention relates to a non-curling multilayer material and particularly to a non-curling photographic multilayer material.

It is known that if a silver halide emulsion layer is applied onto a flexible support, e.g. a film of cellulose acetobutyrate, cellulose triacetate, polyester or polycarbonate, the resulting material on drying exhibits a curling tendency towards the side of silver halide emulsion layer, owing to the tensile forces originating in the silver halide emulsion layer during the drying process. An existing technique for preventing this curling tendency consists of applying a gelatin layer to the back side of the support. This gelatin layer produces tensile forces during the drying process similar to those acting on the front side. In this manner, one can produce a multilayer material which even in dry condition has no curling tendency.

It is also known that the tensile forces of a gelatin layer of a photographic material are considerably enhanced by the presence of silver halide crystals in said gelatin layer. In order to counteract any curling action in such a material, there should be applied to the back side a gelatin layer having a markedly higher proportion of gelatin per unit area of surface than the gelatin silver halide emulsion layer at the front side.

It is further known e.g. from U.S.P. 2,993,792, issued July 25, 1961, to incorporate into the gelatin backing layer inert organic or inorganic insoluble fillers in extremely finely divided state in order to enhance the tensile forces of the backing layer. Thus, a part of the gelatin in the backing layer is replaced by a filler which does not absorb water during the treatment in the processing solutions. In this fashion, the drying time of the backing layer is markedly shortened, so that .one of the disadvantages of a layer having a higher gelatin content is avoided.

During development of a silver halide emulsion layer the silver halide is converted into silver on the exposed areas. Most of the silver halide, however, is dissolved during fixation. Moreover, in photographic colour material even the silver is fully removed by processing.

Especially due to the dissolution of the unaltered silver halide during fixation, the tensile forces of the dry emulsion layer after drying will be much lower than before. This upsets results in a disturbance of the previously attained equilibrium of the tensile forces of front and backing layers and results in a strong curling tendency of the multilayer material towards its back side.

Until now the manufacture of photographic material as described above which shows no curling tendency neither before nor after processing, was considered impossible.

It has now found that this difliculty can be prevented by incorporating into the backing layer macromolecular compounds which enhance the tensile forces in said backing layer and which dissolve during processing in one of the photographic baths. As a result thereof the tensile forces in the backing layer are decreased in the course of processing, so that there results a material which has no curling tendency either before or after processing.

by raising the pH up to 4.65.

A photographic material according to the present invention comprises a support, at least one silver halide emulsion layer on the front side of this support, and on the back side a water-permeable colloid layer containing such an amount of binding agent or binding agent plus inert insoluble filler, that the tensile forces in this layer after processing are equal to those in the layer or layers on the front side.

The invention is characterized in that a macromolecular compound, whose tensile forces considerably decrease or disapppear during the processing, is provided in the backing layer in such an amount, that the tensile forces in this layer before processing are equal to those in the layer or layers on the front side.

The amount of macromolecular compound incorporated in the backing layer is chosen in such a manner that the decrease of the tensile forces at the front side of the support due to the conversion of exposed silver halide into silver and to the fixation of the unaltered silver halide is compensated by the decrease of the tensile forces in the backing layer during treatment in one of the photographic solutions. The decrease or disappearance of tensile forces in the backing layer may be due to the dissolution of the macromolecular compound in one of the photographic processing solutions.

Suitable macromolecular compounds which according to the invention can be incorporated into the backing layer of a photographic material are polymers the solubility of which depends on the pH of the medium. It means they should, e.g. be less soluble in neutral medium, but readily soluble in aqueous mediums with pH-values comparable to those of the usual developing and/or fixing solutions.

As macromolecular compounds soluble in acid medium i.e., in the usual fixing and stop baths, can be used poly(vinylpyridines), poly(vinylquinolines), poly(vinylimidazoles), poly(vinylpyrimidines), poly(vinylamine), poly(vinylaniline), poly(N,N-dialkylaminoalkyl acrylates) poly(N,N-dialkylaminoalkoxyalkyacrylamides etc., and their respective copolymers with hydrophobic ethylenically unsaturated compounds.

Macromolecular compounds which dissolve in alkaline medium i.e., in the commonly used developing solutions, are copolymers of unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid and citraconic acid. If the copolymer comprises an unsaturated dicarboxylic acid, also the half-esters and half-amides thereof may be considered.

Amphoteric polymers insoluble in neutral medium and soluble in alkaline and acid medium are formed by copolymerisation of the afore-rnentioned unsaturated car boxylic acids with the above-mentioned unsaturated basic monomers.

All these monomers comprising acid and/or basic groups can be polymerized with hydrophobic ethylenically unsaturated compounds.

These hydrophobic compounds should be present in the copolymer in such a proportion that the copolymer is rendered insoluble or less soluble by changing the pH. As hydrophobic ethylenically unsaturated compounds are considered: styrene and its derivatives, vinyl chloride, vinylidene chloride, vinyl esters such as vinyl acetate, acrylic acid esters, methacrylic acid esters, acrylonitrile, methacrylonitrile, etc. 7 l

The proportion of hydrophobic groups with respect to other groups in the copolymer naturally determines the pH value at which the copolymer becomes insoluble. If e.g. copoly(2-vinylpyridine/styrene) (:20) is dissolved in a strongly acid medium, it can be precipitated The same copolymer,

however, comprising but 57% of vinyl pyridine, already precipitates at pH 3.95.

The incorporation of these macromolecular compounds into the backing layer may be carried out in several ways. For example, a solution is made consisting of a mixture of gelatin and the macromolecular compound at a pH- value at which both are soluble. Occasionally a surface-active agent may be added. By changing the pH- value of the solution so that the macromolecular compound becomes insoluble, the latter will precipitate in the gelatin solution in a very finely dispersed state. In this form the resulting dispersion can be applied as a backing layer, after the addition of the necessary wetting agents and eventually of antihalation dyes and/ or ingredients commonly used in the manufacture of photographic colloid layers. Obviously, the resulting dispersion may be washed in order to remove the excess of the salts. The washing may be performed according to a known method either after chilling and noodling, or according to a process applied in the preparation of silver halide emulsions by a precipitation method.

According to another method, the macromolecular compound is dissolved in water, whereupon the obtained solution is added to an aqueous solution of gelatin and finally the resulting dispersion is added to the coating composition of the backing layer.

In these processes account should be taken of the fact that the pH-value whereby a polymer is precipitated from its aqueous solutions is influenced by the presence of other polymers in the solution, in this case gelatin. For example an alkaline aqueous solution of copoly(methyl methacrylate/methacrylic acid) (48:52) having an intrinsic viscosity in teterahydrofuran of 0.27 dl./g., precipitates by acidification to pH 4.2. If an equal amount of gelatin having an isoelectric point of 4.8 is also dissolved in the alkaline aqueous solution, the copolymer precipitates at pH 5.1 and below.

According to another method for the preparation of the coating composition, the macromolecular compound can also be dissolved in a non-water-miscible or only slightly water-miscible organic liquid. Said solution is dispersed in an aqueous gelatin solution. If necessary, the resulting dispersion can be washed according to a known method.

It is also possible to use as a water-immiscible liquid a solvent having a boiling point lower than 100 C. This solvent is then removed from the dispersion by heating above the boiling point of said solvent.

According to a further method the monomers can be polymerized in an aqueous solution according to known emulsion polymerization methods. The resulting dispersion can directly be added to the backing layer composition ready for coating.

It is clear that the above-described processes are not restricted to photographic materials using gelatin as a binding agent, but that they also can be successfully applied to materials whereby gelatin is entirely or partly replaced by another water-permeable colloid, e.g. by some gelatin derivatives, poly(vinyl alcohol), half-esters of poly(vinyl alcohol) and maleic acid, etc.

As the tensile forces exhibited by the macromolecular compound should disappear or markedly decrease within the very restricted period of photographic processing, macromolecular compounds should be used the chemical nature and physical behaviour of which are carefully selected. During its very short presence in the photographic solutions, the macromolecular compound should be washed completely away, so that only the tensile forces due to the presence of gelatin only are left in the backing layer after processing. Generally the best results are obtained with macromolecular compounds of low molecular weight, e.g. having an intrinsic viscosity preferably lower than 0.3 dl./ g. although polymers having a higher intrinsic viscosity can also be used. Further, polymer particles sizing less than 4 preferably less than 1p, will yield the best results.

In the above description of the invention, mention has only been made of a simple backing layer. The backing layer, however, may consist of two or more layers with the macromolecular compound being preferably incorporated into the outmost layer. Care should be taken that in this case the total of the tensile forces of the backing layers balances the tensile forces of the front side layer(s), the tensile forces caused by the silver halide crystals being neutralized by the tensile forces caused by the macromolecular compound in the outmost backing layer.

In addition to the macromolecular compound and the binding agent, the backing layer may obviously contain still other substances such as dyes, pigments, antistatic agents, other insoluble fillers, etc.

The binding agents for the silver halide emulsion layer and for the backing layer need not necessarily be the same. Thus e.g. gelatin can be used as a binding agent for the light-sensitive layer, whereas it can entirely or partly be replaced by a synthetic binding agent in the backing layer.

The amount of macromolecular compound which should be used according to the present invention, and the tensile force in the backing layer which off-sets the tensile force of the silver halide crystals in the light-sensitive emulsion layer before the processing may vary within wide limits. This amount is mainly determined by the amount of silver halide present in the light-sensitive layer or layers and by the chemical nature and the physical behaviour of the macromolecular compound itself.

As a binding agent for the light-sensitive silver halide generally 4 to 20 g. of gelatin per sq. m. is used. In special processes, however, minor or major amounts can be used. Care should be taken to use per sq. m. of backing layer nearly the same amount of gelatin as used in the front layer taking into account, however, the known curling tendency of the photographic support. Obviously a part of the gelatin in the backing layer can be replaced by insoluble inert fillers, such as those described egg. in US. patent specification 2,993,793, filed February 15, 1955. The amount of light-sensitive silver halide crystals in the front layer preferably amounts to nearly 3 to 25 -g./sq. m., but larger or smaller quantities may be used. The amount of macromolecular compound should then be selected in accordance with the amount of silver halide present and will be determined by some random tests for each polymer individually. Generally it can be stated that the backing layer should comprise at least 1 g. of polymer per sq. m.

The following examples illustrate the present invention.

Example 1 A low molecular weight copoly(styrene/maleic anhydride) is esterified with a mixture of ethanol and an excess of butanol in such a way that in the resulting copoly- (styrene/monobutyl maleate/monethyl maleate) having an intrinsic viscosity of 0.03 dl./g. still 1.8 m. eq./g. of maleic anhydride groups and 2.9 m. eq./ g. of carboxylic groups are present. Of this copoly(styrene/monobutyl maleate/monoethyl maleate) 16 g. are dissolved together with 0.5 g. of the compound having the formula C17H3 50H (marketed Armour and Company, Chicago, Ill., U.S.A., as a surfactant of the trade-name Ethofat 60/60) in cm. of methylene chloride. While rapidly stirring this solution is emulsified at 32 C. in 300 cm. of a 2% aqueous gelatin solution whereby the temperature is gradually raised to 50C. in order to evaporate the methylene chloride. In this way a suspension of the copolymer in the aqueous gelatin solution is obtained. The particle size of the copolymer suspension is less than Lu. This suspension is poured while stirring in 300 cm. of a 10% aqueous gelatin solution. After addition of antihalation dyes and coating solutions such as wetting agents, hardening agents, etc. the resulting solution is coated as a backing layer to give 14 g. of solid substance per sq. m. onto a cellulose triacetate support which on the front side is provided with a contrasty photographic gelatino-si-lver halide emulsion layer containing 13 g. of silver halide and 9.5 g. of gelatin per sq m.

The thus prepared photographic element is practically free of any curling tendency before as well as after the processing.

A photographic material having a backing layer containing the same amount of gelatin but no copolymer as described above, shows a strong curling tendency towards the emulsion side before processing.

Example 2 27 g. of copoly(methacrylic acid/ methyl methacrylate) (50:50) having an intrinsic viscosity of 0.2 dl./ g. are dissolved in 170 cm. of water of pH 10. This pH-value is maintained during the dissolution by adding 5 N sodium hydroxide. This solution is then poured into 330 cm. of a 10% aqueous gelatin solution at 45 C. of pH 9.5. Whilst rapidly stirring, the mixture is acidified to pH 4 by means of 4 N hydrochloric acid, whereby the polymer fl-occulates in the form of very fine grains. The resulting suspension is chilled, noodled and washed with water for 3 hours. After melting at 45 C., 300 cm. of 7% aqueous gelatin containing an antihalation dye is added to the suspension. After the addition of the necessary coating solutions such as of wetting agents, hardening agents, etc., the mixture is applied to give 10 g. of solid substance per sq. m. onto a polyester support carrying on its front side a contrasty light-sensitive ge-latino-silver halide emulsion layer containing 12 g. of silver halide and 7 g. of gelatin per sq. m.

The resulting material does not curl neither before nor after processing. A comparable material lacking the aforementioned polymer grains and provided with a backing layer containing an amount of gelatin corresponding in tensile forces to those of a material containing both gelatin and copolymer, shows a strong curling effect towards the back side after the processing.

Example 3 A solution of 12 g. of coply(methacrylic acid/ methyl methacrylate) (50:50) of Example 2 in 12.0 cm. of butanol, is emulsified in 400 cm. of a 10% aqueous gelatin solution containing 10 cm. of su'lfonated l auryl alcohol. The resulting dispersion is chilled, noodled and washed for 3 hours with water at 10 C. The noodles are then dissolved again and after addition of the necessary antihalation dyes and coating solutions such as wetting agents, hardening agents, etc. further worked up as described in Example 2. There is practically no difference with regard to the cur-ling effect before and after the processing of the obtained material. An identical material bearing a backing layer which contains only gelatin shows a very strong curling tendency.

Example 4 In a 500 cm. flask fitted with a stirrer, a reflux condenser, a thermometer and a dropping funnel 5 g. of gelatin are dissolved in 300 cm. of water by heating to 50 C. To this solution are added 0.5 g. of sodium bisulfite and 0.5 g. of potassium persulfate. Thereupon a monomer mixture consisting of 25 g. of methacrylic acid, 25 g. of methyl methacrylate and 2 g. of carbon tetrabromide is added dropwise while stirring in a period of 25 minutes. During the exothermic polymerization the temperature in the flask is maintained at 60 C. by cooling in a waterbath. After the dropwise addition, heating is continued for still 2 hours at 60 C. while stirring and a somewhat viscous emulsion of the copolymer is obtained. The conversion of the monomers is quantitative.

Then 80 cm. of this emulsion are added to 380 cm. of a aqueous gelatin solution at pH 5.5. The obtained dispersion is coated to give 12 g. of solid substance per sq. m. on the backing side of a light-sensitive photographic film the light-sensitive emulsion of which contains 11.5 g. of silver halide and 8 g. of gelatin per sq. m. The film shows no curling tendency after processing and drying.

Example 5 27 g. of copoly(methacrylic acid/ methyl methacrylate) (50:50) having an intrinsic viscosity of 0.15 dl./-g. are dissolved at 35 C. in cm. of water and 26 cm of 5 N sodium hydroxide. After dissolution, a mixture of 190 cm. of 20% aqueous gelatin (having a pH 5.8 alone) and 23 cm. of 4 N sulfuric acid is added at 40 C. whilst thoroughly stirring. The pH value of the resulting dispersion is 5.2. After chilling and n-oodling, the dispersion is washed for 3 hours in running water. After melting at 45 C., 300 cm. of 7% aqueous gelatin containing an antihalation dye is added to the dispersion. After adding the required coating solutions such as of Wetting agents, hardening agents, etc. the mixture is coated to give of 9.3 g. solid substanceper sq. m. on a cellulose triacetate support carrying on its front side a contrasty light-sensitive gelatino-silver halide emulsion layer containing 11.5 g. of silver halide and 7 g. of gelatin per sq. m.

The thus-prepared material and a comparable material, which does not include the afore-mentioned polymer but is provided with a backing layer containing 10 g. of gelatin per sq. In. both are initially flat.

After exposure and processing, the material prepared as described above and the comparable material are dried. The latter shows a strong curling tendency towards the back side, whereas the former remains flat.

Example 6 50 g. of copoly(methacrylic acid/methyl methacrylate) (50:50) having an intrinsic viscosity of 0.16 dl./-g. is dissolved in a mixture of cm. of water, 12.5 cm. of ethanol and 12.5 cm of 5 N sodium hydroxide at a temperature of 40 C. While thoroughly stirring this mixture is poured into 250 cm. of 25% aqueous gelatin at 45 C. and pH 5.7. The pH of the resulting dispersion is 5.5. The following compositions are then added successively: 2,440 cm. of 10% aqueous gelatin comprising an antihalation dye and 100 cm. of a 47% aqueous emulsion of copoly(butadiene/methyl met-hacrylate) (40:60). The necessary coating solutions such as of wetting agents, hardening agents, etc. are added and the mixture is then coated to give 8.2 g. of dispersion per sq. m. on a cellulose triacetate support, carrying on its front side a contrasty light-sensitive gelatino-silver halide emulsion layer which contains 11.5 g. of silver halide and 7 g. of gelatin per sq. m. The resultant material and the comparable material comprising 10 g. of gelatin on its back side but without the afore-described polymer, are initially flat.

After image-wise exposure, processing and drying the comparable material shows a strong curling tendency towards the back side, whereas the test material is practically flat.

We claim:

1. Photographic material comprising a supporting film of synthetic polymer, said film carrying on one side at least one silver halide emulsion layer and on the other side a backing layer, said backing layer comprising a water-permeable colloid binding agent substantially insoluble in the photographic processing solutions for said material and a finely divided macromolecular compound dispersed in said binding agent in the amount of 'at least 1 gm. per square meter of film area and sufficient that the collective tensile forces acting on the two sides of said material are substantially equalized before photographic processing, said macromolecular material having an intrinsic viscosity of not more than about 0.3 dl./ gm. and being a polymer of alpha,beta-ethylenically unsaturated monomers which polymer is soluble in a processing solution for said material and thereby dissolves during such processing to substantially equalize the collective tensile forces acting on the material sides after processing.

2. Photographic material according to claim 1, wherein copoly(methacrylic acid/methyl methacrylate) is used as a macromolecular compound.

3. Photographic material according to claim 1 wherein said finely divided particles have an average size of less than about 4 microns.

4. A photographic material as in claim 1 wherein said polymer is selected from the group consisting of a polymer of a basic vinyl monomer, the vinyl group of which bears a radical selected from the group consisting of a basic nitrogen-containing heterocyclic nucleus and a basic nitrogen-containing aliphatic group, and copolymers of said monomer with a hydrophobic vinyl monomer; a copolymer of an alpha,beta-ethylenically unsaturated carboxylic acid with a hydrophobic vinyl monomer; and a copolymer References Cited by the Examiner UNITED STATES PATENTS 7/1961 Beersman et a1. 9685 5/1962 Newman 117-68 NORMAN G. TORCHIN, Primary Examiner.

T. J. HOFFMAN, R. H. SMITH, Assistant Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,300,313 January 24, 1967 Marcel Nicolas Vrancken et al.

r appears in the above numbered pat- It is hereby certified that erro etters Patent should read as ent requiring correction and that the said L corrected below.

In the heading to the printed specification, between line:

9 and 10, insert the following:

Claims priority, application Netherlands, Aug. 14, 1962, 282,075

Signed and sealed this 14th day of November 1967.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

1. PHOTOGRAPHIC MATERIAL COMPRISING A SUPPORTING FILM OF SYNTHETIC POLYMER, SAID FILM CARRYING ON ONE SIDE AT LEAST ONE SILVE HALIDE EMULSION LAYER AND ON THE OTHER SIDE A BACKING LAYER, SAID BACKING LAYER COMPRISING A WATER-PERMEABLE COLLOID BINDING AGENT SUBSTANTIALLY INSOLUBLE IN THE PHOTOGRAPHIC PROCESSING SOLUTIONS FOR SAID MATERIAL AND A FINELY DIVIDED MACROMOLECULAR COMPOUND DISPERSED IN SAID BINDING AGENT IN THE AMOUNT OF AT LEAST 1 GM. PER SQUARE METER OF FILM AREA AND SUFFICIENT THAT THE COLLECTIVE TENSILE FORCES ACTING ON THE TWO SIDES OF SAID MATERIAL ARE SUBSTANTIALLY EQUALIZED BEFORE PHOTOGRAPHIC PROCESSING, SAID MACROMOLECULAR MATERIAL HAVING AN INTRINSIC VOSCOSITY OF NOT MORE THAN ABOUT 0.3 DI./GM. AND BEING A POLYMER OF ALPHA,BETA-ETHYLENICALLY UNSATURATED MONOMERS WHICH POLYMER IS SOLUBLE IN A PROCESSING SOLUTION FOR SAID MATERIAL AND THEREBY DISSOLVES DURING SUCH PROCESSING TO SUBSTANTIALLY EQUALIZE THE COLLECTIVE TENSILE FORCES ACTING ON THE MATERIAL SIDES AFTER PROCESSING. 